Method of simultaneously phosphating and cleaning metal surfaces and composition therefor



Uni d State te METHOD OF SIIVIULTANEOUSLY PHOSPHATING AND CLEANING METALSURFACES AND COM- POSITION THEREFOR Claims priority, application GreatBritain March 31, 1950 6 Claims. (Cl. 148-615) This invention relates toimprovements in the production of phosphate coatings on ferrous and zincor zinc alloy surfaces with solutions of the phosphates of sodium,ammonium, potassium, magnesium or organic bases, or mixtures thereof.

The use is known of such solutions either alone or in the presence ofsuitable oxidizing agents and/or metal accelerators for formingphosphate coatings on ferrous and zinc surfaces.

Such processes are preferably operated at a temperature above 150 F. andwithin the pH range of 4.2 to 5.8 on ferrous surfaces and 3.5 to 5.0 onzinc surfaces. By their use, due to the low acidity of the bath,dissolved metal is precipitated readily as a coating without formingmore than a negligible amount of sludge; consequently such processeshave desirable qualities of low consumption of chemicals, and there islittle or no scaling of the coils and clogging of the spray jets. Due,however, to their low acidity, these processing solutions exert butlittle pickling action on the metal surface and have little power toremove soil or act upon greasy surfaces. Another disadvantage associatedwith this type of process is that the coatings produced sometimes tendto be dusty. It has been proposed to overcome these difiiculties byadding wetting agents, but such a procedure has not proved entirelysatisfactory.

We have now found that ferrous and zinc or zinc alloy surfaces may becleaned and coated simultaneously to give improved coatings of highresistance to corrosion by a process in which there is applied to thesurface an emulsion of a grease removing solvent in an acidic solutionof a phosphate of sodium, ammonium,- potassium, magnesium, or of anorganic base or a mixture of such phosphates. Phosphate solutionscontaining accelerators are preferred, such as, for example, chlorates,bromates, sulfites, nitrites, etc. A quantity of accelerator having aneffect on the coating action substantially equal to that of about .5percent to 4 percent chlorate is satisfactory. The

' grease-removing solvents which we prefer are those which are not veryvolatile at the processing temperature yet do not possess too high aboiling range; otherwise they tend to adhere to the metal surface andprevent processing. We have found that solvents having a boiling rangewithin the limits of 130 C. to 300 C. are most suitable, and any normalgrease-removing solvent within this boiling range and which iscompatible with the solution can be used. We prefer to use aromatichydrocarbons; for example, the fraction known commercially as SolventNaphtha or aliphatic hydrocarbons such as the paraffin fraction knowncommercially as Kerosene. The solvent is preferably present in aconcentration from 1 to 10 percent of the coating solution. Othersuitable solvents are tetrahydro naphthalene, methylcyclohexanone, ethylbenzoate, and orthodichloro benzene.

The maintenance of rapid movement between the solution and the surfaceto be treated is desirable, and it is, therefore, preferred to spray thesolution onto the metallic surface. To maintain the grease removingsolvent in the state of a stable emulsion during the treatment anemulsifying agent is required. We prefer non-ionic materials as theprincipal emulsifying agents. Certain anionic active agents, such aspetroleum sulphonates and long chain alcohol sulphates, may be usedsince they are stable within the required pH range of 3.5 to 5.8.Cationic active agents are less desirable mainly because they inhibitthe phosphate coating action.

By non-ionic oil-in-water principal emulsifying agents we mean thatclass of surface active agents which is used as the main emulsifyingingredient and which remains substantially unionized in aqueous solutionhaving a pH of 3.5 to 5.8. Examples of such agents which we have foundto be particularly, elfective are the derivatives of ethylene oxidepolymers, particularly those containing about 3 to 25 polyoxyethylenegroups therein, such as polyoxyethylene derivatives of oleic acid, whichare commercially available under the name Antarox B-lOO and AccoEmulsifier #5, and polyoxyethylene alkyl phenol derivatives, which areavailable commercially under the name Antarox A, Igepal, and TritonX-100. We have found para iso-octyl phenyl ether polyoxyethylene glycolhaving nine polyoxyethylene groups in the glycol to be particularlyuseful. Further suitable non-ionic emulsifying agents includecondensation products of oleyl alcohol with ethylene oxide, and apolyethylene oxide chain esterified with lauric acid, available underthe names Emulphor O and Brig 30, respectively.

Operation of the process is preferably effected at a temperature above150 F., but satisfactory coatings can be obtained at room temperature onzinc surfaces given a suitable time of treatment. Working at F.satisfactory phosphate coatings can be produced in from one-half to twominutes spray. It is of advantage to rinse the coatings produced with adilute solution of chromic, phosphoric, or oxalic acid; with a dilutesolution of an iron, chromium or aluminum salt-for instance, ferroussulphate, ferric nitrate, chromium sulphate or nitrate, or aluminumsulphate or nitrate; or with a solution containing a mixture of thesesubstances. The concentration of the rinsing solution is suitably from 7to 21 ounces of the acid or salt in 100 gallons water, although moreconcentrated solutions may be employed, and the temperature of therinsing solution is preferably from F. to 180 F. A rinsing period of oneminute is satisfactory, and by the rinsing the resistance of the metalto corrosion is increased, and the tendency of paint applied to thecoating to blister is reduced.

The presence of emulsified solvents in the coating solution enablesphosphate coatings to be formed on metal surfaces which are too greasyand soiled to allow solutions which do not contain emulsified solventsto attack them and produce satisfactory coatings. Even on clean metalsurfaces the presence of the emulsified solvent in the coating solutionenables it to wet the metal surface more readily and so produce coatingsmore even in character with less dust and with greater rapidity.

The invention is illustrated by the following example:

A solution is prepared containing 1.4 percent sodium dihydrogenphosphate and 0.5 percent sodium chlorate. There is then stirred intothe solution 2 percent by weight of kerosene which itself contains 5percent of its weight of para iso-octyl phenyl ether polyoxyethyleneglycol. The solution is adjusted to give a pH of 5.0 and is placed in aspray machine and heated to about F. to F. and sprayed onto a greasyferrous surface for a period of about 1 minute. The metal surface aftertreatment is rinsed in hot water, followed by immersion for half aminute in a solution of 10 ounces chromic acid in 100 gallons of watermaintained at 160 F. before final force drying. By this treatmentslightly iridescent, adherent, even,

corrosion-resistant coatings of approximately 50 mg./ sq. ft: areobtained eminently suitable for use as a base for paints, lacquers orlike materials.

The same treatment when applied to similarly greasy ferrous surfaceswherein the coating solution does not contain emulsified solvent isfound to give substantially no coating.

Byadjusting the above solution to a pH of 4.5 excellent coatings can inlike manner be obtained upon zinc surfaces.

The invention also includes the solutions referred to above, and thesemay be prepared at operational strength, i. e., at a strength suitablefor immediate use in the process, or as concentrated chemicals, i. e.,at, a strength such that they requiredilution before use.

We claim:

1. A process for simultaneously cleaning and producing a phosphatecoating on the surfaces of metal of the group consisting of iron andzinc and their alloys which comprises the steps of (1) applying .to thesurface an aqueous solution of an acidic phosphate of an alkali metal inthe presence of an accelerator having an eifect on the coating actionsubstantially equal to that of about .5 percent to 4 percent chlorate, 1percent to percent of a hydrocarbon solvent, and a non-ionicoil-in-water emulsifying agent of the polyoxyethylenetype having 3 topolyoxyethylene groups therein in an amount sufiicient to form a stableemulsionof. said solvent, said solution having a pH of from 3.5 to 5.8and continuing the application until a coating results, and (2) rinsingthe coated surface with a dilute solution of chromic acid.

2. A process as claimed in claim 1 wherein the emulsifying agent is paraiso-octyl phenyl ether polyoxyethylene glycol having 9 polyoxyethylenegroups in the glycol.

3. An aqueous solution for de-greasing and producing a phosphate coatingon the surfaces of metal of the group consisting of iron and zincand'their alloys which consists essentially of an acidic phosphateselected from the group consisting of sodium phosphate, potassiumphosphate, and ammonium phosphate, and mixtures thereof, an acceleratorin an amount having an effect on the coating action substantially equalto that of about .5 percent to 4 percent chlorate, 1 percent to 10percent of a hydrocarbon solvent having a boiling point within the rangeof 130 C. to 300 C., a polyoxyethylene derivative type emulsifying agenthaving 3 to 25 polyoxyethylene groups therein in an amount sutficient toform a stable emulsion of said solvent, said solution having a pH withinthe range of 3.5 to 5.8.

4. An aqueous solution for degreasing and producing a phosphate coatingon the surfaces of metal'of the group consisting of iron and zinc:andtheir alloys, which consists essentially of an acidic phosphate selectedfrom the group consisting of sodium phosphate, potassium phosphate,ammonium phosphate and mixtures thereof, .5% to 4% chlorate, 1% to 10%of a hydrocarbon solvent having a boiling point within the range of C.to 300 C., para iso-octyl phenyl ether polyoxyethylene glycol having 9polyoxyethylene groups in the glycol in an amount sufficient to form astable emulsion of said solvent, said solution having a pH within therange of 3.5 to 5.8.

5. A solution for degreasing and producing a phosphate coating on thesurfaces of metal of the group consisting of iron and zinc and theiralloys which consists of 1.4% sodium dihydrogen phosphate, .5 sodiumchlorate, 2% kerosene, .1% para iso-octyl phenyl ether polyoxyethyleneglycol having 9 polyoxyethylene groups in the glycol, balance Water, thepH of the solution falling within the range of 3.5 to 5.8.

6. A process for degreasing and producing a phosphate coating on thesurfaces of metal of the group consisting of iron and zinc and theiralloys which comprises the single step of subjecting said surfaces tothe action of an aqueous solution of an acid phosphate selected from thegroup consisting of sodium phosphate, ammonium phosphate, potassiumphosphate and mixtures thereof and having a pH in the range of 3.5 to5.8, 1%10% of a grease-removing hydrocarbonsolvent having a boilingpoint within the range of 130 C. to 300 C. and a non-ionic emulsifier ofthe polyoxyethylene type having 3 to 25 polyoxyethylene groups thereinin an amount sufficient to .form a stable emulsion of said solvent insaid solution.

References Cited in the file of this patent UNITED STATES PATENTS1,949,921 Schweitzer Mar. 6, 1934 2,209,291 Witty July 23, 19402,403,426 Douty et al. July 2, 1946 2,456,947 Iernstedt Dec. 21, 19482,470,136 Bramberry May 17, 1949 2,471,907 Snyder May 31, 1949 2,471,908I Snyder May 31, 1949 2,479,423 Snyder Aug. 16, 1949 2,609,308 GibsonSept. 2, 1952 FOREIGN PATENTS 557,352 Germany Aug. 22, 1932

1. A PROCESS FOR SIMULTANEOUSLY CLEANING AND PRODUCING A PHOSPHATE COATING ON THE SURFACES OF METAL OF THE GROUP CONSISTING OF IRON AND ZINC AND THEIR ALLOYS WHICH COMPRISES THE STEPS OF (1) APPLYING TO THE SURFACE AN AQUEOUS SOLUTION OF AN ACIDIC PHOSPHATE OF AN ALKALI METAL IN THE PRESENCE OF AN ACCELERATOR HAVING AN EFFECT ON THE COATING ACTION SUBSTANTIALLY EQUAL TO THAT OF ABOUT .5 PERCENT TO 4 PERCENT CHLORATE, 1 PERCENT TO 10 PERCENT OF A HYDROCARBON SOLVENT, AND A NON-IONIC OIL-IN-WATER EMULSIFYING AGENT OF THE PHOLYOXYETHYLENE TYPE HAVING 3 TO 25 POLYOXYETHYLENE GROUPS THEREIN IN AN AMOUNT SUFFICIENT TO FORM A STABLE EMULSION OF SAID SOLVENT, SAID SOLUTION HAVING A PH OF FROM 3.5 TO 5.8 AND CONTINUING THE APPLICATION UNTIL A COATING RESULTS, AND (2) RINSING THE COATED SURFACE WITH A DILUTE SOLUTION OF CHROMIC ACID. 